1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming method and a storage medium.
2. Description of Related Art
Conventionally, there is an image forming apparatus which forms an electrostatic latent image on a photoconductor drum by a light emitting diode (hereinafter, called “LED”) head writing optical system in which writing elements such as a plurality of LED or the like are arranged in a line form, and which forms an image by transferring and fixing the toner image which is formed by toner being attached to the electrostatic latent image to a recording medium (hereinafter, called “paper”) such as paper or the like. In this image forming apparatus, a color image is formed on a paper by transferring each color of Y (yellow), M (magenta), C (cyan) and K (black) by the LED head writing optical system in which the writing elements of each color are arranged in a line form so that the colors overlap.
In the image forming apparatus which uses the LED head writing optical system, the image forming to the paper is influenced by dispersion in arrangement of each writing element and by a misplacement of the writing optical system itself. Specifically, when a number of colors are superimposed to form an image, a minor displacement of pixels of each color becomes noticeable as a color shift. Therefore, in the image forming apparatus, a correction of the writing position of the pixels based on the shifting amount measured in advance is carried out.
Particularly, there are a correction to shift the pixel forming position in the main scanning direction/sub-scanning direction based on the shifting amount in the main scanning direction/sub-scanning direction, a correction (hereinafter called “skew correction”) of the image forming position based on the inclining amount of the setting position of the LED head writing optical system, a correction (hereinafter, called “bow correction”) of the pixel forming position based on the dispersion in arrangement of the writing element and the like. Further, JP11-179975A and JP2007-3896A discloses a technique to correct the forming position of the pixel in the image forming apparatus in which a color image is formed on a paper.
In the correction using the above described conventional technique, a phenomenon called jaggy in which the outline portion of the letter appears to be zigzag due to the skew/bow correction can easily occur. However, when an image is formed by superimposing multiple colors, the jaggy which occurred in any one of the colors was not noticeable due to one color being superimposed by the other colors even when the skew/bow correction is carried out.
However, when the image is formed using one color, there is a problem that only jaggy becomes noticeable by carrying out the skew/bow correction because other colors are not superimposed.